As with thermostats for controlling heating systems, thermostats for controlling air conditioning systems have anticipator resistors to improve the stability of the temperature in the controlled space. In air conditioning mode thermostats, the anticipator resistor is connected across the power terminals, so that current flows through it when power is not provided to the air conditioning system. Thus, between on times of the air conditioning, the anticipator resistor slowly heats the air within the thermostat housing causing power to be again applied to the air conditioning system earlier than it would otherwise occur. Since the temperature within the thermostat housing typically lags the space temperature, the anticipator resistor if chosen properly and located within the housing properly, will result in the controlled space temperature to hold closely to the selected temperature setting of the thermostat.
One factor which contributes to the energy efficiency of the air conditioning operation, to the operating life of the air conditioning system, and to the accurate control of the temperature and humidity within the controlled space, is the cycles for the air conditioning system per hour. If the cycling rate is too high, the air conditioning system starts and stops too frequently, which can cause excess wear on the system, and because of the high energy draw and relatively small cooling output associated with the first few minutes of air conditioning system operation, lower energy efficiency. It is customary to select the characteristics of the anticipator resistor, the thermostat's temperature sensing element, and thermostat housing to cause the cycling rate to have some nominal value, one cycle per hour (CPH) being typical.
Air conditioning systems have a variety of designs and efficiencies and controlled spaces have their own thermal characteristics. Because of this, I have found that no one cycling rate is suitable for every installation. Accordingly, it is desirable to provide for adjustment of the cycling rate. At the same time, the adjustment for cycling should ideally be easy for the installer to set initially, and after installation should be difficult for the user to inadvertently change.
I presently have pending U.S. patent application Ser. No. 08/261,369 entitled Thermostat With Adjustment for the Cycling Rate of the Heating Plant, and filed on Jun. 16, 1994, and assigned to the assignee of the present application. In this previous application, I describe and claim a heating control thermostat which allows the installer or user to adjust the cycling rate for the furnace supplying the heat to the controlled space by changing the value of a second anticipator resistor. This previous application describes an invention which is similar in theory to the present application, but which requires different circuit connections. Both that invention and this one allow the installer or user to alter the cycling rate of the temperature control apparatus by simply changing a resistance value in the thermostat circuit.